The present invention relates to waveguide antennae, and more specifically to dielectrically-loaded waveguide antennae.
Base station antennae require control of the beam down-tilting for their system's radiation patterns in order to vary the coverage areas for those systems. This variability is necessary, as different beam down-tilt angles will be needed depending upon the location and altitude of the base station and desired coverage area. FIG. 1 illustrates a base station antenna system 110 having two different degrees of beam or radiation pattern down-tilt. A first coverage area 120 is provided at a first down-tilt angle 122, and a second coverage area 130 is provided at a second down-tilt angle 132. Some mechanism is needed to provide the correct amount of beam down-tilt for a base station antenna.
Conventionally, two different techniques are used to control the beam down-tilt. FIG. 2A shows a first conventional technique in which tilting of the radiation pattern is performed mechanically. In this technique, a system 220 includes a base station antenna 222 disposed on a mechanically-tilting platform 225. The system 220 is shown in an un-tilted orientation (solid line) and a tilted orientation (broken lines). The platform 225 is physically tilted to provide a beam down-tilt which covers the desired area. (e.g., areas 120 or 130 shown in FIG. 1). While relatively straightforward to implement, the system 220 produces distortion, i.e., non-uniformity in the antenna coverage area, which leads to unreliable or lost communication links which have been established via the system 220.
The mounter physically adjusts the orientation of the antenna to point downwards. FIG. 2B shows a second conventional technique in which beam down-tilting is performed electrically using a phased-array antenna. In this technique, a system 250 includes signal divider 252, a bank of phase shifters 2541-254n (collectively referred to as phase shifters 254) and a base station antenna 256. A signal is applied to the input port 252a of signal divider 252, and the signal is divided (e.g., equally) between n branches, where each of the divided signals is phase shifted by a corresponding phase shifter 254. The resulting phase-shifted signals are fed to corresponding antennae in the base station antenna array 256, and collectively the signals form a tilted radiation pattern, as shown in FIG. 1, above. The degree of the beam down-tilt is controlled by the amount of phase shifting applied to the signals. This electrically-based system 250 provides a relatively uniform antenna coverage area and thus avoids the distortion in the antenna coverage pattern produced by the mechanical system 220. However the electrical system 250 suffers from added cost and complexity due to the use of a power divider 252 and phase shifter 254 components. Further disadvantageously, the power handling capability of these components may limit the amount of power the system 250 can transmit.
What is therefore needed is an improved antenna array having controllable beam down-tilt.